Abstract

Geophysical investigation for groundwater in Lokoja metropolis using vetrtical electrical sounding (VES) has been carried out. The objectives are to determine the aquifer types, depth to aquiferous zones and geoelectric layers. These are aimed at combating the incessant borehole failures caused due to poor exploration for groundwater in the area. Result of the VES indicate unconfined aquifers formed within weathered basement and the weathered/fractured basement aquifers. The survey delineated a maximum of four geoelectric layers which corresponds to the topsoil, weathered basement, weathered fractured basement and the fresh basement.The weathered basement aquifer occurs within 3 - layer and 4 - layer lithologic sections. The sections indicate a 3 - layer A and H-type curves and a 4 - layer AA-type curves. The resistivity of the weathered basement aquifer in the 3 - layer lithologic sections range between 6.81 ?m and 166.23 ?m, a depth range of 3.99 m to 22.26 m and a thickness of between 3.40 m and 6.14 m while the 4 - layer sections indicate resistivity varying from 316.62 ?m to 750 ?m, a depth ranging from 18 m to 25 m and a thickness of between 5.0 m and 6.70 m. The weathered/fractured aquifer occurs within 4 - layer lithologic sections. The aquifer shows a 4 - layer AA–type geoelectric model with a resistivity range of 277.60 ?m to 317.50 ?m, a thickness ranging between 3.0 m and 3.7 m and a depth varying from 17 m to 19.20 m. Hence, groundwater in Lokoja is stored in weathered regoliths and in fractured Basement rocks.

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